This section provides background information related to the present disclosure which is not necessarily prior art.
It is widely known to provide an inflatable air-bag which, in the event of an accident situation arising, becomes inflated to provide a protective cushion in front of or adjacent to an occupant of a motor vehicle. Whilst it might be thought that a substantially air-tight air-bag would be preferred for this purpose to ensure that the air-bag remains inflated for a maximum period of time, it has actually been found through practice that it is preferable to include at least one air-vent in an air-bag, since otherwise an occupant would simply rebound from the air-bag when hitting it. An air-bag provided with a vent hole has been found to provide a more appropriate “cushioning effect”, even though the resulting air-bag will, of course, become deflated quite rapidly following initial deployment. However, air-bags are typically deployed, by an appropriate sensor arrangement, at such a time that the air-bag is inflated when an occupant of a seat, to be protected by the air-bag actually moves into contact with the air-bag.
It has been found that ideally the internal pressure of an air-bag or the “cushioning” effect provided by the air-bag should be adjusted depending upon certain perimeters such as, for example, the size of a seat occupant, the position of the seat occupant and whether or not the seat occupant is wearing a seat belt. A seat occupant who is not wearing a seat belt may require a rather “stiffer” air-bag than an occupant who is wearing a seat belt. Similarly, a larger occupant has been found to require a “stiffer” air-bag than a smaller occupant. However, an occupant sitting close an air-bag should be provided with a relative “soft” air-bag if at all possible.
Attempts have been made to provide air-bags with these characteristics by sensing the relevant parameter and by adjusting the amount of gas injected into the air-bag by means of the gas generator. Such arrangements are, however, relatively complex and thus expensive. It has therefore been proposed previously to provide an improved air-bag arrangement having a controllable vent so as to allow venting of the air-bag in dependence upon relevant parameters.
WO2003/006276A3 discloses an arrangement of this general type where an air-bag is provided with a controllable vent formed in the fabric of the air-bag. The vent is normally maintained in a closed position by a fabric element retained by a clamp and the clamp is releasable in response to a signal from a sensor such as a crash-sensor. One particular embodiment disclosed in this document provides a re-entrant tube which extends into the interior of the air-bag from a vent hole, with the free end of the tube defining the controllable vent. The free end of the tube is retained by the clamp and released upon receipt of an appropriate signal from the crash-sensor.
However, it is now considered desirable to provide an improved air-bag ventilation arrangement which is suitable for easier manufacture and quicker ventilation in the event of an accident situation.
It is therefore an object of the present invention to provide an improved inflatable air-bag.